A human being has a need for feeling valued. This need also extends to people who are successful and surprisingly even to those who are enlightened! 

This means we can all touch people by offering sincere praise and appreciation. By so doing you make a positive difference to others and at the same time, you feel good about doing so. 

Sincere and specific praise make people realize that you are authentic. A general positive feedback is better than negative feedback, however, specific feedback is far more valuable.

If you are just trying to be nice by providing some feedback then at least make sure the feedback is sincere. If you do not have any sincere positive feedback to provide then no feedback is better.